I need to store about 600,000 images on a web server that uses NTFS. Am I better off storing images in 20,000-image chunks in subfolders? (Windows Server 2008)
I'm concerned about incurring operating system overhead during image retrieval
Go for it. As long has you have an external index and have a direct file path to each file with out listing the contents of the directory then you are ok.
I have a folder with that is over 500 GB in size with over 4 million folders (which have more folders and files). I have somewhere in the order of 10 million files in total.
If I accidentally open this folder in windows explorer it gets stuck at 100% cpu usage (for one core) until I kill the process. But as long as you directly refer to the file/folder performance is great (meaning I can access any of those 10 million files with no overhead)